Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for at least fifty years and have led to the relatively recent market introduction of a number of superior synthetic lubricants, for example, polyalphaolefins. In terms of lubricant property improvement, the thrust of the industrial research effort on synthetic lubricants has been toward fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index, while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. Viscosity index (VI) is the most common measure that is applied to the decrease in viscosity of petroleum oils with increasing temperature. A series of Pennsylvania oils exhibiting relatively small change in viscosity with changing temperature is arbitrarily assigned a VI of 100, whereas a series of Gulf Cost oils whose viscosities change relatively greatly is assigned a VI of 0. From the viscosity measurements at 40.degree. and 100.degree. C., the VI of any oil sample can be obtained from detailed tables published by the ASTM (ASTM D-2270). 14 Kirk-Othmer Encyclopedia of Chemical Technology 489 (Wiley, 1981). U.S. Pat. No. 4,913,794 to Le et al. teaches a method for improving the viscosity index of a lubricant stock and is incorporated herein by reference for its discussions of viscosity index and lubricant upgrading processes.
U.S. Pat. No. 3,671,598 to Moore relates to the isomerization of adamantane-containing compounds in the presence of sulfuric acid to provide useful traction fluids.
U.S. Pat. No. 3,648,531 to Duling et al. teaches a traction drive containing a fluid comprising an alkyladamantane dimer or an alkyladamantanol dimer.
U.S. Pat. No. 3,671,600 to Moore teaches ethylation of an adamantane nucleus in the presence of a strong acid and BF.sub.3 etherate.
U.S. Pat. No. 3,793,203 to Driscoll et al. discloses polyolefins, paraffins, and polar compounds containing a gemdialkyl substituted back-bone structure which are useful as traction fluids.
U.S. Pat. No. 3,903,001 to Gates et al. and U.S. Pat. No. 4,180,466 to Newingham et al. teach synthetic lubricants for limited slip differentials.
U.S. Pat. No. 3,966,624 to Driscoll et al. relates to a hydrogenated polymeric traction fluid containing a light olefin oligomer and at least one saturated adamantane compound.
U.S. Pat. No. 3,972,243 to Driscoll et al. relates to polyolefins, paraffins, and polar compounds containing a gem-structured backbone structure which are useful as lubricant additives and traction fluid components.
Fluorinated adamantanes are taught in U.S. Pat. No. 4,041,086 to Moore et al. Adamantane-containing ethers are shown in U.S. Pat. No. 4,043,927 to Duling et al.
Ester compounds containing one or two cyclic or bicyclic alkanes which are useful as traction fluids are disclosed in U.S. Pat. No. 4,786,427 to Dare-Edwards.
U.S. Pat. No. 5,085,792 to Narihiko et al. relates to a synthetic traction fluid comprising two substituted cyclohexane nuclei connected through an ester linkage.
U.S. Pat. No. 4,963,292 to Honna et al. discloses a higher carboxylic acid triester of adamantane triol which is said to be a useful ingredient in synthetic lubricants.